1. Technical Field
The present invention relates to a motion state detecting method and a motion state detecting apparatus used to grasp the motion state of, for example, a person or the like.
2. Related Art
Traditionally, the motion or so-called motion state of objects including animals such as humans is detected and the result of the detection is used for observation or control of machines. The machines used for this control range broadly from automobiles, aircraft and ships to industrial robots. Generally, an acceleration sensor or an angular velocity sensor is often used to detect the motion state. This is because detection accuracy is required for the use for the control of machines. Therefore, since power is continuously supplied in the environment of use, the issue of power consumption by the sensor itself tends to have a low priority.
Moreover, there traditionally is a sensor called ball sensor in which a conducting sphere is arranged that is movable in a space surrounded by plural electrodes. Since the conducting sphere is located in a gravitational direction within the space, the way the conducting sphere contacts the plural electrodes varies depending on the tilt and movement of an object to which the ball sensor is attached. Thus, a conducting state or a non-conducting state is created between each of the plural electrodes. Therefore, the tilt and movement of the object to which the ball sensor is attached can be detected by measuring the conducting state or the non-conducting state between the plural electrodes. The power consumption by the ball sensor is small because the ball sensor consumes power in the conducting state. However, since the detection accuracy is decided based on the size of the conducting sphere and the shape of each of the plural electrodes, the ball sensor has a lower detection accuracy than the acceleration sensor or the angular velocity sensor.
Although the detection accuracy and the power consumption may conflict with each other as described above, there is a sensor device having a combination of a sensor unit with a high detection accuracy and large power consumption and a sensor unit with a low detection accuracy and small power consumption, as a method to cope with the conflict . For example, JP-A-11-118587 proposes a technique of realizing an oscillation detecting apparatus in which a conducting sphere is placed in a space surrounded by three electrodes that are insulated from each other and the conducting sphere moves because of oscillation or the like and contacts different ones of the electrodes and thus starts up an electrical oscillation detection unit, so that power consumption is smaller than in the case of constantly keeping the electrical oscillation detection unit started up.
However, in JP-A-11-118587, while the fact that the electrical oscillation detection unit is not started up unless the movement of the conducting sphere and the change in the conducting state between the electrodes occur leads to power-saving, measurement is carried out by the electrical oscillation detection unit and power-saving is not realized at the time of measurement. There is also a problem that oscillation cannot be measured before the electrical oscillation detection unit is started up.